feon-fucking-say
I think you could go to the media with it -- especially if its a smaller community, they'd definitely pick it up. First of all, he's saying "I wish", not "I'm going to kill", so I would file that under freedom of speech.
Second of all, when did schools start policing the internet? Seems a little out of their jurisdiction (yes, even though it involves a principal) -- especially if it was posted from a home computer rather than a school PC.
I think parents need to get back to their job of parenting, not making the school responsible for every little thing. There's a certain point where the power of the school authorities ends and the parental power should begin.